Immunoregulatory aspects of in vivo syngeneic mixed lymphocyte reactions

In vivo manifestations of two types of murine syngeneic MLR have been described. For the first, neonatal thymic cells that normally replicate in the presence of lymphoid non-T cells were observed to induce splenomegaly 4 days after injection into x-irradiated adult mice. The second instance of S-MLR occurring in vivo involves the induction of suppressor cells in popliteal lymph nodes that drain the site of deposition of syngeneic splenic cells. The suppressor cells were seen to be capable of inhibiting formation of CTLs to allogeneic or hapten-modified syngeneic lymphoid cell targets. The suppressor cells were seen to appear within 3 days and to remain detectable at 7 days following injection of the spleen cells. Whole spleen cell populations as well as nylon wool adherent and non-adherent subpopulations were equally competent to induce suppression. Adult thymus cells were less able and lymph node cells as well as haptenated spleen cells were unable to trigger suppression. The possible site of action of the suppressor cells upon the CTL system has been discussed.